Page 1

Research Inventy: International Journal Of Engineering And Science Vol.2, Issue 11 (April 2013), Pp 26-35 Issn(e): 2278-4721, Issn(p):2319-6483, Www.Researchinventy.Com

Investigation of Physical Properties in II-VI Ternary Semiconductors of Sulphides, Selenides And Tellurides 1,

Alla Srivani , 2,Prof Vedam Rama Murthy , 3,G Veera raghavaiah

Assistant professor in Vasireddy Venkatadri Institute Of Technology (VVIT) Engineering College, Andhra Pradesh Professor & Head Of The Department, T.J.P.S College, Guntur, Andhra Pradesh, Head Of The Department, PAS College, Pedanandipadu

Abstract: This work explains recent advances in II–VI Ternary Semiconductor Alloys. Current work has significant potential for low-cost, scalable solar cells. The close interplay among the properties of the materials and their utility in solar cells is also briefly discussed. Almost group II–VI materials are direct band gap semiconductors with high optical absorption and emission coefficients. Group II–VI materials are good candidates for use in solar cells. The Electrical and Optical Properties of II-VI Ternary Semiconductor Alloys from Binary Semiconductor Alloys are derived using Additivity rule with Quadratic expressions. The Electrical and Optical Properties studied in this group are confined to Refractive index, Optical Polarizability, Absorption coefficient and Energy gap. A comparison of these data is made with reported data available. The relative merit of Present method based on refractive indices without recourse to the experimental methods is stressed. Merits of study of this group alloys is also outlined.

Keywords: Semiconductors, II-VI Group, Sulphides, Selenides and Telluride Semiconductor alloys I.

INTRODUCTION

Compound semiconductors formed from II–VI or III–V elements are key materials in plans to harvest energy directly from sunlight in photovoltaic devices. In the search for low-cost alternatives to crystalline silicon, thin film compound semiconductor materials are commonly used, it offer advantages over silicon. It is more efficient to create an electric field at an interface among two different Semiconductor materials, known as a heterojunction. A typical polycrystalline thin film has a thin layer on top known as a „„window‟‟ material if lets almost of the light through the interface to the absorbing layer. The absorbing layer has to have a high absorption to be weak in the generation of current and a suitable band gap to provide good voltage. This work shall focus on II–VI and III–VI materials, and emphasize their potential in solar cells and highlight challenges still to be met. [1] 7.1) CdSxSe1-x The ternary compound CdSxSe1-x is a highly photosensitive material, and finds many practical applications such as in discrete and multielement photo resistors, in optical filters, signal memory devices, laser screens, LSI circuits, Infrared imaging devices, Optoelectronic switches, linear image sensor for digital facsimile page scanners, Electro photography, Image intensifiers and exposure meters. CdSxSe1-x films were deposited by thermal vacuum evaporation using the powders of CdS and CdSe synthesized in laboratory. The films were characterized by x-ray diffraction, optical studies, photo conductivity studies and photo electrochemical studies. By using the appropriate amount of pure selenium powder, sodium sulphide and triply distilled water, sodium seleno sulphate is obtained after heating at 95 0 C for nearly 20 hours. Before the preparation of the CdSxSe1-x thin films, CdSxSe1-x powder was prepared by sintering the appropriate ratio of CdS and CdSe powders in argon atmosphere at 5500 C for 20 min. The substrates used were glass and titanium, the substrate temperature was varied in the range of 300 to 473 K. The thickness of the films were found to be 2.5 m from weighing method. X-ray diffractograms of the CdSe, CdS and CdSxSe1-x films deposited at different substrate temperatures in the range 30 -200°C.indicated reflections corresponding to single phase hexagonal structure. As the substrate temperature is increased, the intensity of the peaks is found to increase. Films prepared at a substrate temperature of 200°C indicated maximum intensity with better crystalline nature [2].

26


Investigation Of Physical Properties 7.2) Zn1-xHgxTe The Electro deposition and characterization of Zn 1-xHgxTe (ZMT) thin films are reported. Many efforts have been focused on hetero structures based on popularly known ternary solid solution Zn 1-xHgxTe (0<x<1) thin films as well as bulk materials. CdTe, HgCdTe and other compounds of II-VI group are sparingly promising materials for use in optoelectronic and high-temperature electronic devices. Ternary alloys of II-VI compounds are potential candidates for the detection of electromagnetic radiation. Zinc mercury telluride, a solid solution has a wide range of band gap tunable among 0 eV and 2.25 ev. Zn 1-xHgxTe thin films Electro deposition offers a low cost, scalable technique for the fabrication of thin films [3]. 7.3 CdSe1-xTex The alloys of CdSe1-xTex compound have been prepared from their elements successfully with high purity and stoichiometry ratio (x=0.0, 0.25, 0.5, 0.75 and 1.0) of Cadmium, Selenium and Telluride elements. Films of CdSe1-xTex alloys for different values of composition have been prepared by thermal evaporation method at cleaned glass substrates heated at 473K under sparingly low pressure of 4×10-5mbar at rate of deposition (3A˚/s), after that thin films have been heat treated under low pressure of 10-2mbar at 523K for two hours [4]. 7.4 Zn1-xHgxTe Zn1-xHgxTe films were deposited on to SnO2 coated glass substrates from an aqueous solution bath of ZnSO4, HgCl2 and TeO2 at bath temperatures among 30°C and 80°C. Well adherent Zn 1-xHgxTe thin films with compositions various among x = 0 to x = 0.4 were obtained. The concern of growth parameters such as Deposition potential, concentration of electrolyte bath, pH and temperature on the properties of the film was studied. X-ray diffraction technique was used to determine composition, crystalline structure and grain size of the films. The films exhibited zinc blend structure with predominant (111) orientation. Optical and electrical studies were also reported and the results are discussed [5]. 7.5 ZnxCd1-xS The electronic and optical properties of Zn xCd1-xS thin films are fabricated using chemical spray method. ZnxCd1-xS thin films are deposited on glass substrates at 420°C substrate temperature. Optical data are recorded in the wavelength range 200-700nm. In addition, the absorption coefficient is determined and correlated with the photon energy to estimate the direct transition energy band gap. The crystalline size and degree of preferential orientation were found to decrease with the increase of Zn Concentration x. Zn xCd1-xS thin films have been prepared by a variety of techniques, including spray pyrolysis, ion beam deposition, molecular beam epitaxial growth and screen printing method [6]. 7.6 Pb1-xSnxTe The optical properties of single-crystal Pb1-xSnxTe thin films in the fundamental absorption edge region were investigated in compositions of 0 < x < 0.24, where x is the mole fraction of SnTe. Two thin film samples with x = 0.70 and x = 0.85 were also studied in an try to confirm the inversion of the conduction and valence bands that had been previously predicted for this narrow-gap semiconductor. The index of refraction n and the absorption coefficient a were determined from transmission and reflection measurements made on films 0.8 to 5.0 microns thick, that were deposited on cleaved (100) faces of KCL rock salt substrates. The optical energy gap was determined from the position of the absorption edge in the absorption spectrum. The index of refraction was obtained using the interference fringe method. The absorption coefficient was calculated from an analysis of the theoretical reflectance R and transmittance T for a thin film on substrate [7]. 7.3 Method of study The refractive index, Optical polarizability, Absorption coefficient and Energy gap of II-VI Semiconductor alloys are evaluated by using Principle of additivity and quadratic expressions. The principle of additivity is used to study Physical properties even at very small compositions. The calculated Properties of refractive index, Optical polarizability, Absorption coefficient and Energy gap versus concentrations was fitted by equations Method 1 A12=A1*x+A2*(1-x) + 1/1000*SQRT (A1*A2)*x*(1-x)

27

(7.1)


Investigation Of Physical Properties Method 2 A12=A1*x+A2*(1-x) +1/1000* SQRT (A1*A2*x*(1-x))

(7.2)

Method 3 A12=A1*x+A2*(1-x) – 1/1000*SQRT (A1*A2)*x*(1-x)

(7.3)

Method 4 A12=A1*x+A2*(1-x) – 1/1000*SQRT (A1*A2*x*(1-x))

(7.4)

Additivity A12=A1*x+A2*(1-x)

(7.5)

Where A12 denotes Refractive index (n 12), Optical Polarizability (α m12), Absorption coefficient (α12) and Energy gap (Eg12). A1 and A2 denotes Refractive index (n), Optical Polarizability (α m), Absorption coefficient (α), Energy gap (Eg) of two binary compounds forming ternary compound. The relations for Optical Polarizability, Absorption coefficient and Energy gap from Wave length and Refractive index values are given in previous III-Nitride Materials

II.

RESULTS

The refractive index values of Ternary semiconductor alloys are calculated by using different expressions of 7.1 to 7.5 for whole composition range (0<x<1) and are presented in tables from 7.1 to 7.8. These values are compared with literature reported data [11, 12]. It is found that calculated values are in good agreement with reported values. Graphs are drawn for all these alloys by taking their composition values on x axis and Refractive index values on y axis. These graphs are given from fig 7.1 to 7.2. The refractive indices at various wavelengths for the binary semiconductors are taken from hand book of Optical constants of solids [14] are presented in table 7.1 to 7.8 along with

and

values. The graphs

drawn between and for these Semiconductors are shown in figures. From these graphs intercept α values and the slope β of the straight line are determined and γ values are calculated. All these values are given from the table 7.1. The evaluated Optical Polarizabilities of Binary Semiconductors by using equation 7.8 are also given from the table 7.6. The computed Optical polarizabilities by new dispersion relations are compared with reported values. The values of Molecular weight (M), density (ρ) and refractive index (n) of the semiconductors which are required for evaluation of αm are taken from CRC Hand book [15]. Table7.1: Optical polarizability, Absorption coefficient and Energy Gap of CdxHg1-xTe X=0.00 Wave length λ

R.I value n

Optical polarizability αm

)

28

Absorption coefficient (α)

Energy Gap e.v


Investigation Of Physical Properties 4133 4158 4235 4315 4370 4426 4543 4699 4900 5120 5277 5488 5765

5.854 5.784 5.576 5.371 5.236 5.105 4.845 4.529 4.165 3.815 3.591 3.320 3.009

2.664 2.678 2.727 2.790 2.844 2.908 3.056 3.175 3.239 3.279 3.313 3.382 3.586

0.601 0.596 0.579 0.559 0.542 0.524 0.486 0.459 0.447 0.439 0.432 0.419 0.387

Calculated 107.7 108 110 111 113 115 118 121 122 123 124 128

Reported 82.03 [12]

2.44 2.4 2.3 2.21 2.14 2.1 2.01 1.83 1.59 1.35 1.21 1.05 1.01

Calculated 1.50

Reporte d 1.42[8]

Table 7.2- Optical polarizability, Absorption coefficient and Energy Gap of CdxHg1-xTe X=0.20 Wave length λ 4133 4275 4428 4592 4769 4959 5166 5391 5636 5904 7293 8266

R.I Value n 5.854 5.472 5.100 4.742 4.397 4.066 3.747 3.441 3.148 2.869 1.880 1.463

4.943 4.757 4.547 4.375 4.235 4.118 4.022 3.940 3.871 3.815 3.635 3.457

Optical polarizability αm 0.254 0.266 0.282 0.296 0.309 0.321 0.331 0.340 0.348 0.355 0.379 0.407

Calculated 80.0

Reported 81.17 [12]

Absorption coefficient (α) 2.657 1.943 1.645 1.389 1.170 0.984 0.822 0.684 0.566 0.465 0.591 0.220 0.193 0.112

Energy Gap e.v

Calculated 1.35

Reported 1.75[8]

Table7.3: Optical polarizability, Absorption coefficient and Energy Gap of CdxHg1-xTe X=0.29 Wave length λ ) 4133 4275 4428 4592 4769 4959 5166 5391 5636 5904 7293 8266

R.I Value n

5.854 5.472 5.100 4.742 4.397 4.066 3.747 3.441 3.148 2.869 1.880 1.463

4.781 4.582 4.404 4.258 4.135 4.032 3.945 3.872 3.815 3.758 3.509 3.404

0.264 0.279 0.294 0.307 0.319 0.330 0.339 0.348 0.355 0.362 0.398 0.416

Optical polarizability αm

Absorption coefficient (α)

Calculated 78.2

2.604 2.539 2.478 2.424 2.378 2.336 2.300 2.269 2.244 2.218 2.159 2.334

Reported 80.23 [12]

Energy Gap e.v

calculated 1.42

Reported 1.85[8]

Table7.4: Optical polarizability, Absorption coefficient and Energy Gap of CdxHg1-xTe

29


Investigation Of Physical Properties X=0.43 Wave length λ

R.I Value n

Optical polarizability αm

Absorption coefficient (α)

Energy Gap e.v

) 4133 4275 4428 4592 4769 4959 5166 5391 5636 5904 7293 8266

5.854 5.472 5.100 4.742 4.397 4.066 3.747 3.441 3.148 2.869 1.880 1.463

4.605 4.430 4.280 4.159 4.047 4.957 3.881 3.820 3.747 3.686 3.422 3.341

0.277 0.291 0.305 0.317 0.328 0.338 0.347 0.355 0.364 0.372 0.413 0.427

Calculated 79.44

Reported 79.40 [12]

2.239 1.911 1.626 1.379 1.666 0.982 0.823 0.687 0.670 0.654 0.099 0.090

Calculate 1.30

Reported 1.05[8]

Table7.5: Optical polarizability, Absorption coefficient and Energy Gap of CdxHg1-xTe X=0.76 Wave length λ

R.I Value n

Optical polarizability αm

Absorption coefficient (α)

Calculated 81.49

2.032 1.738 1.481 1.258 1.064 0.898 0.753 0.626 0.178 0.274 0.172 0.102

Energy Gap e.v

) 4133 4275 4428 4592 4769 4959 5166 5391 5636 5904 7293 8266

5.854 5.472 5.100 4.742 4.397 4.066 3.747 3.441 3.148 2.869 1.880 1.463

4.483 4.328 4.195 4.081 3.985 3.903 3.838 3.761 3.696 3.665 3.368 3.283

0.287 0.300 0.313 0.324 0.335 0.344 0.352 0.362 0.371 0.375 0.422 0.438

Reported 78.83 [12]

Calculated 1.25

Reported 1.65[8]

Table7.06: Optical polarizability, Absorption coefficient and Energy Gap of CdxHg1-xTe X=0.86 Wave length λ ) 4133 4275 4428 4592 4769 4959 5166 5391 5636 5904 7293 8266

R.I Value n

5.854 5.472 5.100 4.742 4.397 4.066 3.747 3.441 3.148 2.869 1.880 1.463

4.343 4.208 4.092 3.992 3.909 3.837 3.758 3.690 3.658 3.546 3.313 3.287

Optical polarizability αm

0.299 0.312 0.323 0.334 0.344 0.352 0.362 0.372 0.376 0.393 0.432 0.447

Calculated 79.20

Reported 78.04 [12]

Absorption coefficient (α)

1.801 1.543 1.317 1.120 0.949 0.801 0.671 0.582 0.464 0.377 0.153 0.091

Energy Gap e.v

Calculated 2.30

Reported 2.05[8]

Table7.07: Optical polarizability, Absorption coefficient and Energy Gap of CdxHg1-xTe

30


Investigation Of Physical Properties X=0.99 Wave lengt h λ ) 4133 4275 4428 4592 4769 4959 5166 5391 5636 5904 7293 8266

R.I Value n

5.854 5.472 5.100 4.742 4.397 4.066 3.747 3.441 3.148 2.869 1.880 1.463

4.196 4.084 3.987 3.906 3.823 3.746 3.696 3.595 3.500 3.425 3.225 3.153

0.313 0.324 0.338 0.344 0.354 0.364 0.371 0.388 0.400 0.412 0.449 0.464

Optical polarizability αm

Absorption coefficient (α)

Calculated 77.96

5.873 5.042 4.290 3.677 3.114 2.625 2.208 1.817 1.497 1.222 0.500 0.297

Reported 77.16 [12]

Energy Gap e.v

Calculate d 2.50

Reported 2.36[8]

Table7.08: Optical polarizability, Absorption coefficient and Energy Gap of CdxHg1-xTe X=1.00 Wave R.I Optical Absorption Energy Gap lengt Value polarizability coefficient e.v h n αm (α) λ ) 4133 4275 4428 4592 4769 4959 5166 5391 5636 5904

5.854 5.472 5.100 4.742 4.397 4.066 3.747 3.441 3.148 2.869

4.050 3.961 3.872 3.787 3.783 3.635 3.519 3.440 3.378 3.322

0.328 0.338 0.348 0.359 0.365 0.379 0.397 0.410 0.420 0.431

Calculated 75.66

Reported 76.33 [12]

5.678 4.889 4.181 3.559 3.032 2.541 2.106 1.745 1.440 0.180

Calculate d 2.45

Reported 2.67[8]

Table 7.09 CdSxSe1-x Composition x

1-x

R.I Method1

R.I Method2 2.457

R.I Method 3 2.457

0.00

1.00

2.457

0.36

0.64

0.58

2.457

2.457

2.408

2.408

2.407

2.406

2.400

0.42

2.377

2.378

2.376

2.376

2.368

0.79

0.21

2.348

2.348

2.347

2.347

2.342

1.00

0.00

2.319

2.319

2.319

2.319

2.319

31

R.I Method4

R.I Reported[9]


Investigation Of Physical Properties Table7. 10 Zn1-xCdxTe Composition X

1-x

R.I Method1

R.I Method2 3.56

R.I Method 3 3.56

0.00

1.00

3.56

0.20

0.80

0.40

R.I Method4

R.I Reported[9]

3.56

3.56

3.348

3.349

3.347

3.347

3.348

0.60

3.137

3.137

3.135

3.134

3.136

0.50

0.50

3.031

3.031

3.029

3.028

3.030

0.60

0.40

2.925

2.925

2.923

2.922

2.924

0.80

0.20

2.712

2.713

2.711

2.711

2.712

1.00

0.00

2.50

2.50

2.50

2.50

2.50

Table 7.11 CdSe1-xTex Composition X

1-x

R.I Method1

R.I Method2

R.I Method 3

R.I Method4

R.I Reported [9]

0.00

1.00

2.46

2.46

2.46

2.46

2.46

0.20

0.80

2.468

2.469

2.468

2.467

2.467

0.40

0.60

2.476

2.477

2.475

2.475

2.475

0.60

0.40

2.484

2.485

2.483

2.483

2.483

0.80

0.20

2.492

2.493

2.492

2.491

2.491

1.00

0.00

2.50

2.50

2.50

2.50

2.50

Table 7.12 CdSxSe1-x Composition X

1-x

α -Pol Method1

α -Pol Method2

α -Pol Method3

α –Pol Method4

0.00

1.00

83.855

83.855

83.855

83.855

α –pol Reported [9] 83.855

0.36

0.64

79.043

79.062

79.007

78.988

79.035

0.58

0.42

76.092

76.111

76.055

76.036

76.078

0.79

0.21

73.269

73.288

73.244

73.255

73.256

1.00

0.00

70.439

70.439

70.439

70.439

70.439

Table 7.13 Zn1-xCdxTe Composition X

1-x

α -Pol Method1

α -Pol Method2

α -Pol Method3

α –Pol Method4

0.00

1.00

95.971

95.971

95.971

95.971

α –pol Reported [9] 95.971

0.20

0.80

97.449

97.474

97.418

97.394

97.434

0.40

0.60

98.921

98.946

98.873

98.848

98.897

0.50

0.50

99.653

99.678

99.604

99.579

99.628

0.60

0.40

100.384

100.409

100.336

100.311

100.36

0.80

0.20

101.839

101.863

101.807

101.783

101.823

1.00

0.00

103.286

103.286

103.286

103.286

103.286

32


Investigation Of Physical Properties Research on Physical properties of II-VI Ternary Semiconductor alloys is due to operating characteristics of Semiconductor devices depending critically on the physical properties of the constituent materials. The theoretical study has been made on II-VI Ternary Semiconductor alloys as a function of composition x. The various applications of II-VI Semiconductor Alloys of CdSxSe1-X, CdSe1-xTex, Zn1-xHgxTe, CdxHg1Te as Electronic, Optical and Optoelectronic devices are determined by elementary material properties of x Refractive index, Optical Polarizability, Absorption coefficient, Energy gap and Mobility. Photonic crystals, wave guides and solar cells require knowledge of refractive index and Energy gap of all above Arsenide Group alloys. The Energy gap of Semiconductor alloys determines Threshold for absorption of photons in semiconductors. Refractive index is measure of transparency of Semiconductor alloys to incident radiation. Refractive index and Energy gap of Ternary Semiconductor alloys has significant impact on Band structure. High absorption coeďŹ&#x192;cient Semiconductor alloys can be used for fabricating in thin ďŹ lm hetero junction photovoltaic (PV) devices. Applications on these Ternary Semiconductor Alloy span from communications to biomedical engineering. Narrow band gap semiconductor alloys allow Hetero junction Bipolar Transistors to present terahertz (THz) operation capability. Sensors of this type exploit the unique piezoelectric, polarization characteristics, as well as the high temperature stability of wide-band gap semiconductors in order to allow stable operation with high sensitivity. Using this material system one can also explore the possibility of developing fundamental sources operating in the Terahertz regime and employing Micro-Electro Mechanical Systems (MEMS) approaches. Recent progress and new concepts using narrow and wide-band gap Ternary semiconductor alloys of CdSxSe1-X, CdSe1-xTex, Zn1-xHgxTe, CdxHg1-xTe and device concepts such quantum wells with very high mobility and plasma waves will lead in Terahertz detectors and emitters. Semiconductors of this type may also be used for other novel applications such as spintronics and field emission. Terahertz signal sources based on super lattices have explored applications cover a wide range of devices, circuits and components for communications, sensors and biomedical engineering. Research on Physical properties of II-VI Ternary Semiconductor alloys is due to operating characteristics of Semiconductor devices depend critically on the physical properties of the constituent materials.The Refractive index of Group II-VI Arsenide Semiconductor alloys of CdSxSe1-x reduces significantly from 2.457 to 2.319 by adding a small amount of Sulphur to CdSe and also in Zn1-xCdxTe Refractive index decreases from 3.56 to 2.50 by adding small amount of Cadmium to ZnTe. But Refractive index of CdSe1-xTex increases from 2.46 to 2.50 by adding small amount of Tellurium to CdSe. This occurs due to the large disparity in the electro negativity and the atomic size The binding which was totally covalent for the elemental Semiconductors, has an ionic component in II-VI Arsenide Ternary semiconductor alloys. The percentage of the ionic binding energy varies for various Semiconductor alloys. The percentage of ionic binding energy is closely related to electro negativity of the elements and varies for various compounds. The electro negativity describes affinity of electrons of the element. In a binding situation the more electro negative atoms will be more strongly bind the electrons than its partner and therefore carry net negative charge. The difference in electro negativity of the atoms in a compound semiconductor gives first measure for Energy gap. A more electro negative element replacing a certain lattice atom will attract the electrons from the partner more strongly, become more negatively charged and thus increase the ionic part of the binding. This has nothing to do with its ability to donate electrons to conduction band or accept electrons from the valence band.Mobility at high doping concentration is always decreased by scattering at the ionized dopants. Band gap increases with Electro negativity difference between the elements. Bond strength decreases with decrease of orbital overlapping. Electrons are more stabilized by more electro negativity atom. . Semiconductor Materials with higher absorption coefficients more readily absorb photons, which excite electrons into the conduction band. Knowing absorption coefficients of various II-VI Ternary Semiconductor alloys of CdSxSe1-x, CdSe1-xTeX, Zn1-xCdxTe, CdxHg1-xTe, ZnxCd1-xS aids engineers in determining which material to use in their solar cell designs. The absorption coefficient determines how far into a material light of a particular wavelength can penetrate before it is absorbed. In a material with a low absorption coefficient, light is only poorly absorbed, and if the material is thin enough, it will appear transparent to that wavelength. The absorption coefficient depends on the material and also on the wavelength of light which is

33


Investigation Of Physical Properties being absorbed. II-VI Ternary Semiconductor Alloys have a sharp edge in their absorption coefficient, since light which has energy below the band gap does not have sufficient energy to excite an electron into the conduction band from the valence band. Consequently this light is not absorbed. The plot of hν versus (αhν)2 of III-Arsenide Ternary Semiconductor alloys of CdxHg1-xTe at various concentrations of Cd forms a straight line, it can normally be inferred that there is a direct band gap, measurable by extrapolating the straight line to the α=0 axis. On the other hand, if a plot of hν versus αhν1/2 forms a straight line, it can normally be inferred that there is an indirect band gap, measurable by extrapolating the straight line to α=0 axis. Measuring the absorption coefficient for Ternary Semiconductor Alloys gives information about the band gaps of the material. Knowledge of these band gaps is extremely important for understanding the electrical properties of a semiconductor. Measuring low values of Absorption coefficient (α) with high accuracy is photo thermal deflection spectroscopy which measures the heating of the environment which occurs when a Semiconductor sample absorbs light. The energy levels adjust with alloy concentration, resulting in varying amount of absorption at different wavelengths in II-VI Ternary Semiconductor alloys of CdSxSe1-X, CdSe1-xTex, Zn1-xHgxTe, and CdxHg1-xTe. This variation in optical properties is described by the material optical constants, commonly known as Refractive index (n). The optical constants shape corresponds to the material‟s electronic transitions. Thus, the optical constants become a “fingerprint” for the semiconductor alloys. The Optical Polarizability of II-VI Ternary Semiconductor alloys CdSxSe1-x reduces significantly from 83.855 to 70.439 by adding a small amount of Sulphur to CdSe, and in Zn1-xCdxTe Optical Polarizability increases from 95.971 to 103.286 by adding small amount of Cadmium to ZnTe. This occurs due to the large disparity in the electro negativity In II-VI Ternary Semiconductor alloys replacing existing atom with high Atomic number results in Decreasing of Energy gap due to increase of charge carriers with increase of mobility and by replacing existing atoms of low atomic number result in Increase of Energy gap due to decrease of charge carriers transmitting from valence band to conduction band with decrease of mobility.

34


Investigation Of Physical Properties

ACKNOWLEDGEMENT: Foremost, I would like to express my sincere gratitude to my advisor Prof Vedam Ramamurthy for the continuous support of my Ph.D study, Management members of my working college of VVIT and Head of the Science and Humanities department

References:[1]. [2]. [3]. [4]. [5]. [6]. [7]. [8]. [9]. [10]. [11]. [12]. [13].

Zimmer, J. P.; Kim, S. W.; Ohnishi, S.; Tanaka, E.; Frangioni, J. V.; Bawendi, M. G. J. Am. Chem. Soc. 2006, 128, 2526-2527 Reddy R.R., Rama gopal k., Narasimhulu k., Siva Sankara Reddy L., “Interrelationship between structural, optical, electronic and elastic properties of materials., Journal of Alloys and Compounds 473 (2009) 28–35 Mahalingam T., Kathalingam A., Velumani S., Soonil Lee., Hosun Moon., Yong Deak Kim., “Electrosynthesis And Studies on Zn1-xHgxTe Thin Films, Journal of New Materials for Electrochemical Systems 10, 21-25 (2007) Bard, A. J.; Faulkner, L. R. in Electrochemical Methods: Fundamentals and Applications, 2nd Ed. John Wiley & sons: New York, 2001, p 290 Suparna Sadhu and Amitavapatra “Synthesis and spectroscopic study of high quality alloy Cd xZn1-xS nanocrystals., J. Chem. Sci., Vol. 120, No. 6, November 2008, pp. 557–564. Becerril M*, Silva-Lopez H, and Zelaya-Angel O., “Band gap energy in Zn-rich Zn1-xCdxTe thin films grown by r.f. sputtering. REVISTA MEXICANA DE F ISICA 50 (6) 588–593 DECEMBER 2004. Venu gopal Rayapati , Ping-I Lin, and Yit-Tsong Chen Photoluminescence and Raman Scattering from Catalytically Grown ZnxCd1-xS Alloy., J. Phys. Chem. B 2006, 110, 11691-11696 http://www.cleanroom.byu.edu/EW_ternary.phtml-BRIGHAM YOUNG UNIVERSITY, Department of Electrical and Computer Engineering, “Direct Energy Band Gap in Ternary Semiconductors”. Sathyalatha K.C PhD Thesis”Optical and related properties of few II-VI and III-V Semiconductors” SKU University, Anantapuram (2012) 10)Murthy V.R, Jeevan kumar.R and Subbaiah, D.V., “New dispersion relation: Relation to ORD, MORD and Molecular Polarization‟ Proc viii Annual conference on IEEE/EMBS, Texas, XIV, P. 1636-1639 (1986). Edward D. Palik, Handbook of Optical Constants of Solids, Volume 2, Academic press, 21 march 1991 William M. Haynes, David R. Lide, CRC Hand book of Physics and chemistry, Taylor & Francis Group, 91 st Edition, 26-May2010. Ravindra N M, preethi Ganapathi, Jinsoo choi Energy gap-Refractive index relations in Semiconductors- An overview Department of physics, New jersey institute of technology, New york, USA, Infrared physics and Technology (2006).

35

E0211026035  
Read more
Read more
Similar to
Popular now
Just for you